A Prefrontal ‘Mind’s Eye’

As you are driving, a car lurks in your blind spot. Where in your brain do you “keep it in mind?” Researchers now suggest that one key region is the so-called frontal eye field (FEF), part of the prefrontal cortex. Long associated with the guidance of eye movements, the FEF now appears not to be an “eye” field at all. Researchers have found evidence that the FEF contains a map of space around the body, in which we can keep any object—visual or auditory, real or imagined—“in mind,” even if we also happen to be viewing or hearing something else.

“I think the FEF is best modeled as a map of prioritized space, or a map of locations that are important,” says Clayton Curtis, a psychologist and cognitive neuroscientist at New York University. “These are locations we might want to look at.”

Curtis and Ph.D. student Kyeong Jin Tark co-authored a study to justify the view that the FEF represents a relatively abstract map of attentional space; it appeared online on Oct. 4 in Nature Neuroscience.

They used functional magnetic resonance imaging of 13 people to show that an auditory object—a simulated sound source produced with stereo earphones—causes sustained FEF activity when the “source” is within the subjects’ visual fields.

That fit with previous observations from brain-electrode studies in monkeys, and was in keeping with the FEF’s supposed role in guiding eye movements to locations of interest. But Tark and Curtis then moved the auditory source “off the map”—out of the subjects’ visual fields and even behind their heads. They expected to see the FEF activity drop off. “To our surprise, we found that FEF activity persisted,” says Curtis.

“The fact that you can see that kind of attentional map, even behind the head where there’s no way you can be planning an eye movement, is pretty strong evidence that it’s not a simple notion of [eye-related] motor planning,” says David Badre, a Brown University neuroscientist who studies the role of the prefrontal cortex in working memory, attention and other functions, and who was not involved with this research. He agrees that the definition of the FEF as an “eye field” probably does need to be broadened. “Something like a salience map or an attentional map does make a lot of sense for that region of the brain,” he says.

Curtis’s lab is performing further fMRI-based experiments “to test hypotheses about how the brain represents the unseen space behind your body, and to test hypotheses about the various frames of reference that the brain uses for coding space,” he says.

As Badre notes, researchers also would like to work out the relationships between the FEF and other brain regions that map space. “One thing that Clay’s and others’ work has shown is that there are lots of these spatial maps that are computed in the frontal cortex and parietal cortex. Each one has a different origin. Some are coarser [in resolution], some are finer,” he says.

And though we might have the sense of experiencing a single mental operation when we mentally focus on a particular location in space, really we are experiencing the collective workings of these networked cortical regions.

“Our notions of attention, imagination, mind’s eye and so forth, really are an emergent property of these network computations,” says Badre.